KMO及STAT3表現量在犬黑色素瘤預後角色之探討

Abstract

犬黑色素瘤是犬常見罹患的腫瘤之一，惡性黑色素瘤最容易發生的部位為口腔。由於，犬黑色素瘤的腫瘤型態極為多變，且黑色素形成的數量亦多變。目前，犬黑色素瘤缺乏良好的生物標誌協助腫瘤診斷其惡性程度及預後。Kynurenine 3-monooxygenase (KMO) 是參與在tryptophan代謝過程中kynurenine pathway中的一個酵素，位於粒腺體的外膜，可將kynurenine降解為3-hydroxy kynurenine。在過去的研究中，KMO的表現量分別與腫瘤的惡性程度和病畜生存時間具有相關性。在許多癌症的研究中指出，轉錄訊息傳遞及活化子蛋白3 (signal transducer and activator of transcription 3, STAT3) 參與kynurenine的生成。許多文獻也指出在人類與犬隻的多種癌症當中，STAT3與惡性腫瘤的發生及發展密切相關，其調控細胞增生、存活、促進腫瘤細胞的轉移、侵襲及血管新生。由於STAT3和KMO都與癌症進展相關，因此進一步驗證它們與臨床腫瘤診斷上的應用性，我們自國立臺灣大學生農學院附設動物醫院收集85例犬黑色素瘤，並以免疫化學組織染色研究KMO, STAT3和磷酸化STAT3 (p-STAT3) 蛋白質的表現量是否和該腫瘤的各項臨床特性相關。結果顯示，在所有腫瘤中皆有KMO蛋白質的表現情況，其中有83％的犬惡性口腔黑色素瘤具有KMO蛋白質高度表現的情況，相較於無KMO或KMO蛋白質低度表現的犬黑色素瘤，具有KMO蛋白質高度表現的腫瘤，其病畜術後的存活時間顯著較短 (P<0.05)。除了KMO外，STAT3和p-STAT3蛋白質的表現也與犬惡性口腔黑色素瘤相關。相較於無STAT3蛋白質表現的犬黑色素瘤，具有STAT3高度表現的腫瘤，其病畜術後的存活時間也顯著較短 (P<0.05)。然而，在相較於無p-STAT3蛋白質表現和具有p-STAT3高度表現的犬黑色素瘤，其兩組的病畜術後的存活率並未達顯著差異。我們也發現，KMO蛋白質表現量與STAT3及p-STAT3蛋白質表現量呈現高度正相關 (P<0.001)。因此，這項研究顯示KMO和STAT3與犬黑色素瘤的惡性具有相關性，推論可作為診斷腫瘤惡性或評估病畜預後狀況的生物標誌物。

Canine melanoma is commonly diagnosed in dogs, and malignant melanoma is reported the most common location in oral cavity. Canine melanoma diagnosis is challenge due to the variety of tumor histological appearances, and furthermore the distinction between benign and malignant melanocytic tumors is not always easy. Therefore, investigating biomarkers for defining the malignancy of melanoma is important for prognostic prediction. Kynurenine 3-monooxygenase (KMO), mainly found on the outer membrane of the mitochondria, is one of the enzymes in the kynurenine pathway. The high expression of KMO in canine mammary tumor and human hepatocellular carcinoma was found to relate to tumor malignancy and short survival time. Many cancers were found their overexpressed signal transducer and activator of transcription 3 (STAT3) is involved in kynurenine production, by which kynurenine is the target substrate of KMO. Since both STAT3 and KMO are prognostic factors of cancers, to validate the interaction between them may facilitate us dissect the mechanisms of tumor development. The results indicated that the expression of KMO was observed in all tumors and 54% were strong KMO expression. Eighty-three percent of patients with strong KMO expression were oral malignant melanoma and patients with KMO strong expression display significantly reduced survival rates when compared to patients with KMO negative or weak protein expression (P<0.05). Comparing to KMO investigations, increasing STAT3 and p-STAT3 manifestation was also shown to correlate with oral malignant melanoma. The patients with STAT3 positive display significantly reduced survival rates when compared to patients with STAT3 negative expression (P<0.05). However, the patients with p-STAT3 protein expression in two groups were not significantly correlated with survival rates. The KMO expression was significantly and positively correlated with STAT3 and p-STAT3 protein expression (P<0.001). The evidence of this study may support KMO and STAT3 are correlated with malignant phenotype of canine melanoma and could be biomarkers in diagnosis or prognosis in canine melanoma. It might be involved in the same pathway (in mitochondrial) and/or through the metabolism of tryptophan.